The invention relates to a guide blade for a turbomachine, preferably for a turbine and even more preferably a gas turbine, for use, for example, in a power station for generating electricity. The invention also preferably relates to a guide blade ring made up of such guide blades. The invention relates, even more preferably, to a component for bounding a flow duct in a turbomachine.
Such a gas turbine has a shaft or a rotor to which so-called rotor blades are permanently connected. The rotor blades extend in the radial direction into a flow duct of the turbine. A plurality of rotor blades form a rotor blade ring in the peripheral direction of the rotor. A plurality of rotor blade rings are arranged at a distance from one another in the longitudinal direction of the rotor. So-called guide vanes, which extend in the radial direction from, the outside into the flow duct, are arranged on the turbine casing. The guide vanes are likewise arranged in guide vane rings, the individual guide vane rings meshing with the rotor blade rings in the manner of teeth. In contrast to the rotor blades, the guide vanes are solidly and immovably fastened on the casing.
The flow duct enclosed between the rotor blades and the guide vanes is bounded by the guide vanes and rotor blades and is sealed toward the outside. For this purpose, both the rotor blades and the guide vanes have, as a rule, a so-called platform in the region of their blade/vane root, with which they are fastened to the rotor or to the casing. This platform extends essentially at right angles to their blade/vane aerofoil, which protrudes radially into the flow duct.
Very high temperatures occur, particularly in the case of gas turbines in the field of electricity generation. Efforts are made to achieve continually higher gas temperatures in the course of efficiency increases. This increases the demands made on the materials used and on the cooling, which is generally necessary, of the individual components of the gas turbine.
An impingement cooling system for a gas turbine blade/vane is revealed in DE 26 28 807 A1. The gas turbine blade/vane is aligned along a blade/vane axis and has a blade/vane aerofoil and a platform region along the blade/vane axis. In the platform region, the platform extends transverse to the blade/vane axis away from the blade/vane aerofoil outward approximately at right angles. In this way, the platform forms a part of the flow duct for a working fluid (hot gas), which flows through the gas turbine. Due to the very high temperatures in the flow duct, the surface of the platform exposed to the hot gas is subjected to severe thermal effects. In order to cool the platform, a perforated wall element is arranged in front of the surface of the platform facing away from the hot gas. Cooling air enters via the holes in the wall element and meets the surface of the platform facing away from the hot gas. This achieves efficient impingement cooling.
WO 97/12125 A1 shows a sealing element for sealing a gap between components of a gas turbine installation. Two blades/vanes directly adjacent to one another in a blade/vane ring have mutually opposite grooves on opposing edges of their platforms. A sealing element is inserted into these grooves. A gap between the platforms is sealed by this sealing element. At the same time, however, the platforms are not rigidly connected to one another so that sufficient clearance remains for thermal expansions in particular. The sealing element has a profiled surface area and this provides an improved sealing effect.
In addition to being subjected to thermal effects, the rotor blades must withstand high centrifugal forces during operation because of the rotational speed of the rotor. This applies particularly to turbines which are employed as propulsion engines or propulsion turbines, for example in the aeronautical field. Particularly high rotational speeds are provided for such propulsion turbines. Because of the high centrifugal forces associated with the high rotational speeds, efforts are made to achieve the lowest possible mass of the rotor blades, particularly in the case of these propulsion turbines. For this purpose, U.S. Pat. No. 3,294,364 proposes separating the platform from the individual guide blades, i.e. to dispense with an integral unit, consisting of rotor blades and platform, and its advantages. For the multi-part configuration demands, as compared with the integral unit, increased complexity and therefore increased time and cost requirements during the assembly of the rotor blades in the turbine. The separation between the platform and the actual rotor blade is, for example, known from U.S. Pat. No. 5,244,345.
An object of the invention is to provide a guide blade for a turbomachine which can be manufactured simply and at favorable cost. A further object of the invention is to provide a guide blade ring made up of such guide blades and to provide a component for bounding a flow duct in a turbomachine.
According to the invention, the object directed towards the guide blade is achieved by means of a guide blade for a turbomachine, which guide blade is aligned along a blade/vane axis and has a blade/vane aerofoil arrangement, a fastening region and a platform region arranged between the blade/vane aerofoil region and the fastening region. The platform region is preferably designed to receive a separating region which can be separated non-destructively from the guide blade. The separating region is preferably part of a platform, which is associated with the platform region, for bounding a flow duct in the turbomachine.
The guide blade is therefore no longer configured integrally, as was previously usual in the case of guide blades, but has a platform region which can be separatedxe2x80x94the separating region. This multi-part design therefore initiates a new way of constructing guide blades. In contrast to the rotor blades for aircraft turbines, for which such a multi-part construction is known, the construction does not appear to be appropriate for guide blades of a gas turbine in the field of electricity generation. On the one hand, there are of course no centrifugal forces in the case of the guide blades and, on the other, the assembly complexity and therefore the expenditure of time and cost are disadvantageously influenced by the multi-part construction.
In a surprising manner, however, the multi-part design leads to a marked simplification of the manufacturing process for the guide blade per se. Particularly in the case of one-piece cast guide blades, this is due to the casting process being very much simpler because at least part of the platform, which usually protrudes at right angles to the blade/vane axis, does not have to be cast at the same time. This results in a casting mold which is very much simpler to handle and manufacture. This simplification of the casting process is important, particularly in the case of single-crystal or directionally solidified guide blades. Such guide blades have very good material properties. Because attempts are made to achieve continually higher operating temperatures for gas turbines in the field of electricity generation, it is usually only possible to employ such high-quality guide blades.
A further essential advantage of the multi-part configuration for the manufacturing process may be seen in the fact that the individual parts have clearly simplified geometry as compared with the integral configuration. This permits the application of a high-quality coating which protects the turbine guide blades from damage, in particular from thermal damage due to the desired high temperatures. In the case of the integral configuration, a high-quality and enduring coating is only possible with great difficulty in the transition region between the blade/vane aerofoil and the platform extending essentially at right angles to it because, in this transition region, it is almost impossible to achieve a uniform coating, such as is possible in the case of a simple geometry, in particular in the case of a flat shape.
Material pairing is, furthermore, at best only possible in a very limited manner in the case of an integral design. For both reasons, cost and the different, in particular thermal, demands made on the various blade/vane regions, however, it can be advantageous to use different materials for various regions of the blade/vane. This applies particularly to the platform. Because of the independent embodiment of at least a part of the platform as a separating region, this separating region can be manufactured from a material which is different from the rest of the blade/vane material. Manufacture with an independent separating region is of particular advantage in the case of a guide blade, in which the platform has to receive, at most, a small part of loads which occur during an employment of the guide blades in a turbomachine. The fastening region is then advantageously configured in such a way that it receives the essential part of these loads. Because of this, no particular measures have to be taken for a particularly stable and permanent connection when attaching the separating region at the platform region.
The separating region can be advantageously attached by means of a blading-side edge, with the platform region and the blading-side edge being configured in such a way that they mesh together, in particular over the complete length of the blading-side edge, when the separating region is attached.
Such meshing together achieves good fixing of the separating region on the platform region. In addition, meshing together seals the separating region and the platform region against a working medium or against a cooling medium. The working medium, in particular hot gas, is guided within the flow duct of the turbomachine whereas the cooling medium for cooling the platform flows onto the platform on the surface remote from the flow duct surface.
In addition, the blading-side edge and the platform region preferably mesh together as groove and tongue. This is particularly simple from the point of view of manufacturing technology and also permits simple installation of the blade/vane in the turbomachine.
An intermediate piece can be advantageously introduced between the platform region and the blading-side edge, which intermediate piece seals a gap, which remains between the separating region and the platform region after the attachment of the separating region. A gap remaining between the platform region and the separating region is therefore sealed, by means of such an intermediate piece, against entry of the working medium flowing in the flow duct. The intermediate piece can also, however, reduce or prevent entry of a cooling medium into the flow duct. In addition, a mechanical fixing of the separating region on the platform region can also be achieved by means of the intermediate piece. This is preferably achieved by both the blading-side edge and the platform region having a groove. These grooves are located opposite to one another during an attachment of the separating region. The intermediate piece can be laid in the grooves, in particular over the complete groove length. When the separating region is attached, therefore, the two opposing grooves form a channel into which the intermediate piece is introduced. This corresponds to the arrangement of the sealing element between the platforms of two adjacent blades/vanes, as follows from WO 97/12125 A1 cited further above.
The platform advantageously has an area extension, the separating region having a proportion more than 70% of this area extension. In consequence, a major part of the platform is configured in the form of the separating region. More than 90% of the platform is preferably configured as the separating region. The platform is therefore an independent component to a major or even almost complete extent.
A stiffening rib preferably extends from the separating region, in particular approximately at right angles to an area extent of the separating region. This stiffening rib is connected to the fastening region when the separating region is attached. Such a stiffening rib serves to provide an additional mechanical stabilization of the platform in the turbomachine. The stiffening rib preferably meshes into the fastening region, and in particularxe2x80x94as described for the separating region and the platform regionxe2x80x94by means of a groove and tongue configuration or by means of an intermediate piece introduced into the opposing grooves. By this means, the separating region is also fixed to the fastening region in addition to being fixed on the platform region. An extension approximately at right angles of the stiffening rib relative to the area extension of the separating region provides mechanical fixing in a direction approximately at right angles to the fixing direction in the platform region.
The guide blade is preferably designed as a gas turbine guide blade of a gas turbine in a power station for generating electricity. As already mentioned, the gas turbine guide blade is subjected to particularly severe thermal effects due to the hot gas flowing in the flow duct, i.e. the hot gas duct. The platform, too, is subject to these severe thermal effects. The at least partially separate design of the platform as an independent component, the separating region, immediately achieves several advantages, of which the essential ones are briefly summarized once again:
1. The separating region can be manufactured from a material which is different from the material of the rest of the guide blade because it does not have to be cast together with the rest of the guide blade. As an example, the separating region can be manufactured from a ceramic material. The separating region can also include a metallic material, or an alloy, which is different from the material of the rest of the guide blade.
2. Gas turbine guide blades are frequently provided with a coating system for protection against oxidation and/or corrosion and for protection against overheating. Due to the separate embodiment of the separating region, a different coating system can be provided for the separating region and for the rest of the vane to match different thermal effects. In addition, this coating can be applied more simply and with a higher quality because the blade/vane and the separating region can be respectively coated separately. Particularly in the case of plasma spraying, it is important to align the surface to be coated as nearly as possible at right angles to the plasma beam. In the case of oblique spraying, increased porosity occurs on the coating and, therefore, increased susceptibility to flaking. The separate embodiment of guide blade and platform by means of the separating region makes it possible to place both the guide blade and the separating region substantially at right angles to the plasma jet during the coating operation.
3. The platform cooling is frequently effected by arranging impingement cooling sheets on the side of the platform remote from the hot gas duct. Such sheets have openings by means of which the cooling air is fed at right angles onto the platform surface to be cooled. In the case of a guide vane with a completely integral configuration, it can be difficult to apply such impingement cooling sheets. Problems particularly occur when a double platform is provided. In the double platform, a platform part on the hot gas side undertakes the screening from the hot gas whereas a load-carrying platform part opposite, in the radial direction, to this platform part on the hot gas side undertakes the receiving of the load. In such a double-platform concept, relatively little space remains between the platform parts so that welding on platform cooling sheets is complex and difficult. In the case of a separating region which is separate, these difficulties do not arise because the separating region can be provided with impingement cooling sheets or further means, for example turbulators or ribs, in a simple manner and independently of the rest of the blade/vane.
4. The transition region between the blade/vane aerofoil and the platform is a critical region with respect to the thermal effects because radiusing, and therefore an accumulation of material, occurs in this region. This transition region is difficult to cool and, because of the accumulation of material, is subjected to particularly severe thermal stresses at the same time. Due to the separate embodiment of the separating region, this transition region can now be cooled effectively and in a simple manner. This takes place by feeding cooling air through a gap between the separating region and the platform region. The cooling air therefore flows through this gap directly past the critical transition region and cools the latter in the process.
According to the invention, the object directed toward a guide blade ring is achieved by means of a guide blade ring with guide blades according to one of the above embodiments, the separating region respectively associated with a guide blade being arranged between two guide blades immediately adjacent to one another.
That part of the platform which is located in each case between two adjacent guide blades is therefore configured as a separating region. The complete guide blade ring is therefore built up from guide blades with separating regions introduced separately between them. The advantages of such an assembly follow in a manner corresponding to the above statements with respect to the advantages of the guide blades.
Two guide blades immediately adjacent to one another are preferably associated respectively with a single, common separating region. In consequence, each of the two guide blades share a separating region located between them. In other words, each two guide blades have a common platform region which is located between them. This results, in particular, in a simplification with respect to manufacture technology because the number of components is reduced.
According to the invention, the object directed toward a component is achieved by a component for bounding a flow duct in a turbomachine, which component can be introduced between two immediately adjacent guide blades of a guide blade ring and can be connected to these guide blades.